1. Field of the Invention
This invention relates to lift trucks and, more particularly, to a stabilizing system for the mast to reduce torsional forces between the mast and the chassis.
2. Description of the Prior Art
Lift trucks of conventional and/or specialized design have a pair of mast uprights pivotally connected to the chassis of the vehicle near the lower portions thereof. When certain types of loads are carried on the forks projecting from the mast, such as when long loads or when heavy loads are carried by the forks on the mast, extreme torsional forces are placed upon the mast tending to twist the mast relative to the chassis of the vehicle as the vehicle traverses an uneven terrain. This can cause excessive flexing of the mast structural members and joints causing fatigue failures and a breakdown of the machine or causing the loads on the forks to be dumped or dropped.
Heretofore, there have been many attempts made to provide protective guards for the operator of the lift truck, which guards take the form of structural shields connected to the chassis and, frequently, to the lift uprights so as to hold a guard member over the head of the operator.
One such patent is the patent to Watson, U.S. Pat. No. 2,754,019, issued July 10, 1956, which shows a protective guard carried by the masts and by a pair of supports from the chassis of the vehicle. The patent to Dalecke et al. U.S. Pat. No. 2,263,981, issued Nov. 25, 1941, also has a pair of members connected to the mast with a pair of supports connected to the rear of the vehicle to support a guard over the head of the operator. The patent to Dayton, U.S. Pat. No. 3,199,699, issued Aug. 10, 1965, provides not only for the mast being fixed, but also for various mechanisms for holding a load on the forks including a rigid member extending between the mast and the chassis of the vehicle, which rigid member is intended to protect the operator and to lock the mast in a vertical position.
The Watson and Dalecke et al. patents do not provide any stabilizing means for the mast. The Dayton patent, even if it could be said to serve as a stabilizing means, locks the mast in a vertical operating position and is not capable of permitting the mast to be tilted relative to the vehicle as is required in conventional lift operations.